Polybutene continuous metal casting lubrication process



United States Patent 3,397,734 POLYBUTENE CONTINUOUS METAL CASTING LUBRICATIGN PROCESS John S. Brown, Flossmoor, 111., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana No Drawing. Filed May 31, 1966, Ser. No. 553,699 2 Claims. (Cl. 164-73) This invention relates to the continuous casting of ferrous metals and particularly to lubricants for use therein.

The continuous casting of ferrous metals has become a very important development in steel making, especially for converting molten steel into usable solid form. In the continuous casting technique, the molten metal is initially shaped in a water-cooled mold, usually of copper, wherein the molten steel coming into contact with the molding surfaces of the mold forms a thin, solid skin around the core of molten steel. Due to the high melting point, high specific heat, and low thermal conductivity of ferrous metals, especially steel, and because thermal contraction causes the skin to separate from the mold wall shortly after solidification, the rate of heat abstraction from the casting is so low that molten metal persists within the interior of the casting for some distance below the mold. Heat abstraction from the casting is effected by spraying the casting with water after the casting leaves the mold. Inasmuch as the mass of the casting is positively removed from the mold by driven pinch rolls, any tendency for the casting to adhere to the mold wall may cause the skin to rupture. A rupture of the skin within the mold may heal itself before the casting leaves the mold. However, breakouts frequently occur because the rupture has not healed before the casting leaves the mold. A breakout releases molten metal and forces a shutdown of the operation. Accordingly, mold lubricants are used to prevent adherence of molten metal to the molding surfaces during the initial cooling of the molten metal and formation of the solid skin.

Conventional lubricating materials used for mold lubrication, such as mineral lubricating oils or naturally occurring oils of vegetable, animal or marine origin, such as rapeseed oil, are unsatisfactory. Decomposition of such lubricants immediately occurs when contacted by the hot molten ferrous metal, at temperatures in the neighborhood of 2,800 to 3,000 F. Decomposition products from such materials is in the form of dense black smoke that obscures the operation, and carbon residues on the solidified metal surface. Such carbon residues are very undesirable for discoloration of the metal surface occurs which is not removable by subsequent operations. Inasmuch as copious amounts of water are directly sprayed on the metal casting after emergence from the mold to complete the solidification, any oil remaining on the surface of the casting becomes emulsified in the cooling water. Consequently, there is a substantial separation of residue oil from the cooling water. Further, the rate of decomposition of such materials is non-uniform, and thus the incomplete barriers to prevent adherence of the cooling metal to the molding surface occurs. In other words, there is incomplete film formation between the metal surfaces which produce rupture in the thin, solid skin, which ruptures may not heal before the casting emerges from the mold. Therefore, it is highly desirable that the lubricant material produce a complete uniform film of the molding surface when the molten metal initially contacts the mold. Further, the products of decomposition should not interfere with the visibility of the operations nor form undesirable residues on the solid metal surfaces. It is also essential that the lubricant be readily and easily separable from the water coming in contact with the casting.

3,397,734 Patented Aug. 20, 1968 It has been discovered that liquid polybutenes are unique materials for preventing adherence of molten metal to the cooled molding surface of the mold. It has been found that these materials function as hydrodynamic lubricants in the continuous casting operation. The liquid polybutenes are liquid hydrocarbons prepared by polymerizing butenes from a butane butylene stream as described, for example in US. Patents 2,407,873 and 2,677,000-1-2. The liquid polybutenes suitable for use in the present invention are commercially available products having a viscosity in Saybolt Seconds Universal (SSU) at 210 F. of from about 30 to about 22,000. The liquid polybutenes are slowly decomposed in situ by the heat from the molten steel to a gas without the formation of any carbonaceous residues. The gas, thus formed, acts as a barrier and also as a lubricant between the molding surface and the molten or solidified metal. Accordingly, the molten steel, as it passes through the mold, is initially in contact with a liquid polybutene film which is gradually converted to gas which forces the solidifying metal away from the mold surfaces. The gaseous decomposition products are colorless, and consequently there is no effect upon the visibility of the operation. Thus, the visibility and air-pollution problems associated with conventional lubricants is avoided. Further, any residue liquid polybutenes remaining on the casting surface after emergence from the mold do not emulsify in the secondary cooling water and are readily separable therefrom. The fact that the liquid polybutenes leave no residue after decomposition is extremely desirable and advantageous because metal surface discoloration or contamination is thereby avoided.

While liquid polybutenes, having a viscosity from about 30 to about 22,000 SSU at 210 F. are satisfactory for use in the present invention, the liquid polybutenes having a viscosity from about 30 to about 1100 SSU are preferred.

In accordance with the present invention, liquid polybutene having a viscosity of about 30 SSU at 210 F. was used as the lubricant in a six-strand continuous casting machine producing 4 x 4 inch square steel billets. The billets obtained were free of surface residues or defects and metal discoloration. A small amount of the liquid polybutene was found in the used cooling water and was readily separated therefrom.

I claim:

1. In the continuous process of casting ferrous metals wherein molten ferrous metal is initially shaped in a watercool'ed mold, the step of introducing a liquid polybutene, having a viscosity in Saybolt Seconds Universal (SSU) at 210 F. of from about 30 to about 22,000, between the molding surface and molten metal to prevent adherence of the metal to the molding surface.

2. The process of claim 1 wherein said polybutene has a viscosity of from about 30 to about 1,100.

References Cited UNITED STATES PATENTS 2,376,518 5/1945 Spence l6473 X 2,677,001 4/1954 Fragen 260683.15 2,825,947 3/1958 Goss 16473 2,923,041 2/1960 Ryznar 16472 3,034,186 5/1962 Holshouser 16473 3,098,042 7/1963 Morway et al 25259 X 3,220,070 11/ 1965 Tajkowski 164-73 3,298,951 1/1967 Guminski 25259 X 3,298,954 1/1967 Brown 25259 X J. SPENCER OVERHOLSER, Primary Examiner.

R. S. ANNEAR, Assistant Examiner. 

1. IN THE CONTINUOUS PROCESS OF CASTING FERROUS METALS WHEREIN MOLTEN FERROUS METAL LIS INITIALLY SHAPED IN A WATERCOOLED MOLD, THE STEP OF LINTRODUCING A LIQUID POLYBUTENE, HAVING A VISCOSITY IN SAYBOLT SECONDS UNIVERSAL (SSU) AT 210*F. OF FROM ABOUT 30 TO ABOUT 22,000, BETWEEN THE MOLDING SURFACE AND MOLTEN METAL TO PREVENT ADHERENCE OF THE METAL TO THE MOLDING SURFACE. 